1. Field of Invention
The present invention relates generally to devices and methods for measuring time-resolved concentration and/or size distribution of particulate matter emitted in the exhaust of an internal combustion engine.
2. Description of Related Art
Internal combustion engines (e.g., diesel engines) typically generate an exhaust flow that contains varying amounts of particulate matter. The amount and size distribution of particulate matter in the exhaust flow tends to vary with engine operating conditions, such as fuel injection timing, injection pressure, or the engine speed to load relationship. Adjustment of these conditions may be useful in reducing particulate matter emissions and particulate matter sizes from the engine. Reducing particulate matter emissions from internal combustion engines is environmentally favorable. Currently, however, no device exists for determining the mass concentration and the size distribution of the particulate matter in the exhaust of an operating engine in the field (e.g., on-board a vehicle) and in real time.
A device for determining the real-time mass concentrations of particulate matter in the exhaust emission of an internal combustion engine may be useful for controlling operation of the engine. For example, time-resolved mass concentration measurements of particulate matter may be used to provide feedback to a control system for adjustment of operating conditions of the engine to reduce the mass concentration of the particulate matter. These time-resolved measurements may also be used to monitor particulate matter emission compliance in the field and/or to calibrate engine operating parameters.
The angular dependence of the intensity of light scattering from an aggregate of particles (e.g., particulate matter) may be used to determine mass concentrations. A device that measures angular dependence of the intensity of light scattering from an aggregate of particles is generally known as a nephelometer. Nephelometers are typically used to measure the size and concentration of particles in gases or liquids. Research grade nephelometers have been used in research environments for measuring mass concentrations in exhaust emissions from engines. Research grade nephelometers, however, are typically large (e.g., about the size of a small refrigerator) and not usable in the field (i.e., on-board a vehicle). The size of a nephelometer may be related to the number of detectors used to measure the scattering intensity at multiple angles. For example, a typical research grade nephelometer uses 36 detectors for measuring scattering intensity at 36 different angles. In addition, research grade nephelometers may include large external laser systems that are not suitable for use in the field.
A device for monitoring mass concentrations and size distributions of particulate matter in the exhaust of an internal combustion engine may be simple, compact, and inexpensive so that the device can be used on the exhaust system of an engine in the field. The device may withstand the severe operating conditions of the exhaust system (e.g., temperature, corrosion, etc.) and be resistant to fouling from particulate matter buildup.